1. Field of the Invention
The invention relates to copper-based alloy wires and manufacturing methods thereof, and more specifically to copper-based alloy wires utilized for the wire bonding of packages of electronic devices and manufacturing methods thereof.
2. Description of the Related Art
Wire bonding is an extremely important step in the packaging processes of integrated circuit (IC) devices and light-emitting diodes (LED). Bonding wires provide not only signal transmission and power transmission between chips and chip carriers (substrates), but also heat dissipation. Therefore, it is necessary for metal wires for wire bonding to have not only excellent electrical conductivity and thermal conductivity, but also sufficient strength and ductility. It is necessary for the metal wires to have good antioxidative activity and corrosion resistance because the polymer encapsulants for packaging commonly have corrosive chloride ions and hygroscopic properties for absorbing moisture from the environment. Moreover, the metal wire conducts a high volume of heat to the first bond (ball bond) when the ball bond cools from a molten state to room temperature, and thus a heat-affected zone is formed in the metal wire near the ball bond. Grain growth happens to the metal wire in the heat-affected zone due to heat build-up, resulting in the formation of local coarse grains. The local coarse grains result in less strength, and thus the metal wire cracks in the heat-affected zone during the wire pull test, negatively affecting the bonding strength. When completing the packaging processes of the integrated circuit devices or the light-emitting diodes, the high current density through the metal wires can potentially activate atoms in the metal wires and thus generate electron migration during utilization of the packaged products. As a result, holes are formed at the terminal of the metal wires, resulting in a decrease in electrical conductivity and thermal conductivity, and even the occurrence of broken wires.
The bonding wires presently utilized in the electronic industry are mainly pure gold and pure aluminum (referring to George G. Harman, Reliability and Yield Problems of Wire Bonding in Microelectronics, National Institute of Standards and Technology, 1991 by International Society for Hybrid Microelectronics, p. 49-89.). Recently, pure copper wires (referring to US20060186544A1 and U.S. Pat. No. 4,986,856) and composite metal wires such as copper wires with gold plating (referring to U.S. Pat. No. 7,645,522B2), copper wires with palladium plating (referring to US 20030173659A1), copper wires with platinum plating (referring to US 20030173659A1) and aluminum wires with copper plating (referring to U.S. Pat. No. 6,178,623B1) are also being utilized as bonding wires. The internal structure of the conventional metal wires for wire bonding are all equi-axial fine grains. The conventional fine grain structure may provide sufficient tensile strength and ductility. However, there are a lot of high-angle grain boundaries existing between the fine grains. The high-angle grain boundaries scatter the electron transmission, and thus increase the electrical resistivity of the metal wires and simultaneously decrease the thermal conductivity of the metal wires. Additionally, the high-angle grain boundaries have higher interfacial energy and provide favorable paths for environmental oxidation, sulfuration and chloride ion corrosion, lowering the reliability of packaged electronic products. Moreover, the heat-affected zone tends to be formed in the metal wire with a fine grain structure near the first bond (ball bond) during wire bonding. Thus the wire bonding strength is decreased, and electron migration tends to occur to the metal wire with a fine grain structure during the utilization of packaged semiconductor devices or light-emitting diodes, which are all main factors causing the deterioration of the quality and reliability of conventional packaged products utilizing wire bonding technology.
Thus alloy wires and manufacturing methods thereof are required to solve the described problems.